1. Technical Field
The present invention relates to a method for driving a liquid droplet ejecting head and a liquid droplet ejecting device for ejecting liquid droplets of an ink or the like.
2. Related Art
As the liquid droplet ejecting device, there is an ink jet recording device having an ink jet recording head as the liquid droplet ejecting head. Moreover, as the ink jet recording device, in addition to the thermal system, there are those using the piezoelectric system using a piezoelectric element such as a piezo element.
As the ink jet recording device using a piezoelectric element, there are those using the so-called drop-on-demand system, in which ink liquid droplet is ejected from the nozzle top end communicating with a pressure generating chamber by changing internal pressure of the pressure generating chamber by changing the volume (capacity) of the pressure generating chamber by carrying out expansion, contraction or the like of the pressure generating chamber filled with an ink by means of a piezoelectric element.
In general, an ink jet recording head is provided with a switching element per piezoelectric element so as to control the ink liquid droplet ejection from the nozzle by applying/stopping a driving voltage according to on/off operation of the switching element.
Therefore, the ink jet recording head needs to connect a signal line for driving the switching element connected for each piezoelectric element. Moreover, in the case the number of the switching elements for controlling the drive of one piezoelectric element is increased, the signal lines are required for the number of the switching elements. Moreover, due to the concentration of the piezoelectric elements accompanied by the high density of the nozzles, the wiring is complicated so that the wiring work becomes difficult as well.
In order to realize the recent drop size modulation (liquid droplet volume modulation) aiming at the high image quality recently, plural driving waveforms should be generated at the same time, and therefor, the number of the switching elements is increased as well as the number of the wirings between an IC as a set of the switching elements and a control substrate is increased so as to complicate the process.
As to the wiring from the control substrate to the switching element IC, a method realizing the droplet size modulation by successively generating plural driving waveforms in one cycle of the printing and controlling the IC so as to select an arbitrary driving waveform, has been proposed.
However, in this proposal, independent wirings are required for each piezoelectric element, accordingly, with respect to a large number of nozzles and the high density, the wiring complication between the switching element and the piezoelectric element cannot be solved. Moreover, as it will be described later, due to the long driving waveform, it is not suitable for the high speed printing.
On the other hand, as a method for reducing parts and the wirings between the piezoelectric element and the switching element, an ink jet printer that drives piezoelectric elements per block (plural driving elements are divided into plural blocks), has been proposed.
For the ink jet recording device, as in the case of the other image recording devices, high image quality and high speed are required.
As mentioned above, in the ink jet recording device, the printing gradation can be improved by the dot size modulation (liquid droplet modulation) for adjusting ejection droplet amount by controlling the waveform of the driving voltage (driving waveform) to be applied to the piezoelectric element, or the like, moreover, by high density of the nozzles provided for ejecting the ink liquid droplets to the ink jet recording head, the printing speed can be improved as well as the high image quality can be achieved.
However, in the piezoelectric element type ink jet recording device, a driving waveform whose length is a several tens of μsec for controlling the pressure fluctuation in the ejector is needed. In the conventional art, the dividing number of the blocks is limited depending upon the length of the driving waveform to be generated in a printing cycle. Moreover, there is a problem in that, for each block, the impact position of the liquid droplet onto a recording paper can be displaced per block according to the number of the division of the resolution.
Moreover, in the thermal system, because of short driving time (voltage application time), plural pressure generating elements may be driven using the matrix drive system by time sharing, according to the piezoelectric element such as the piezo element, however, for the piezoelectric element such as the piezo element, pressure wave control in the ejector is needed, therefore, it is difficult to shorten the driving time compared with the pressure generating element of the thermal system. Therefore, in order to apply a predetermined driving waveform to plural piezoelectric elements in one printing cycle, the number of the piezoelectric elements is limited. Moreover, there is a problem in that the printing speed is made sacrifice for applying a predetermined driving waveform to each of the piezoelectric elements so that the high speed can hardly be achieved.